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From: Josef Bacik <>
Cc: Eric Sandeen <>
Subject: [PATCH] btrfs: set tree_root->node = NULL on error
Date: Tue, 30 Jun 2020 14:53:02 -0400
Message-ID: <> (raw)

Eric reported an issue where mounting -o recovery with a fuzzed fs
resulted in a kernel panic.  This is because we tried to free the tree
node, except it was an error from the read.  Fix this by properly
resetting the tree_root->node == NULL in this case.  The panic was the

BTRFS warning (device loop0): failed to read tree root
BUG: kernel NULL pointer dereference, address: 000000000000001f
RIP: 0010:free_extent_buffer+0xe/0x90 [btrfs]
Call Trace:
 free_root_extent_buffers.part.0+0x11/0x30 [btrfs]
 free_root_pointers+0x1a/0xa2 [btrfs]
 open_ctree+0x1776/0x18a5 [btrfs]
 btrfs_mount_root.cold+0x13/0xfa [btrfs]
 ? selinux_fs_context_parse_param+0x37/0x80
 btrfs_mount+0x147/0x3e0 [btrfs]
 ? cred_has_capability+0x7c/0x120
 ? legacy_get_tree+0x27/0x40
RIP: 0033:0x7f5302f851be

Fixes: b8522a1e5f42 ("btrfs: Factor out tree roots initialization during mount")
Reported-by: Eric Sandeen <>
Signed-off-by: Josef Bacik <>
 fs/btrfs/disk-io.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 7c07578866f3..c27022f13150 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2592,10 +2592,12 @@ static int __cold init_tree_roots(struct btrfs_fs_info *fs_info)
 		    !extent_buffer_uptodate(tree_root->node)) {
 			handle_error = true;
-			if (IS_ERR(tree_root->node))
+			if (IS_ERR(tree_root->node)) {
 				ret = PTR_ERR(tree_root->node);
-			else if (!extent_buffer_uptodate(tree_root->node))
+				tree_root->node = NULL;
+			} else if (!extent_buffer_uptodate(tree_root->node)) {
 				ret = -EUCLEAN;
+			}
 			btrfs_warn(fs_info, "failed to read tree root");

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Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-30 18:53 Josef Bacik [this message]
2020-07-01  6:23 ` Nikolay Borisov
2020-07-01 18:05 ` David Sterba

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